The invention relates to a boom structure on a work machine, the work machine comprising a cabin and the boom structure.
Various boom structures are employed on work machines for various purposes, generally for attaching various tools to the work machine, in particular, when tools need to be moved and they are required to have good reach in different directions even without relocating the work machine. These tools include, for instance, various lifters, grapples, buckets, cutting-off and/or cutting means and hammers. In forest work units, such as harvesters, forwarders or combinations thereof, boom structures are typically employed in connection with harvester heads used for wood handling, such as delimbing and cutting, and with grabs or grapples used for timber loading. Boom structures may be implemented in a variety of ways, typically, for instance, as articulated boom structures, by controlling movements of degrees of freedom through pressure-medium-operated actuators such as hydraulic cylinders. Often boom structures of this kind may also be called manipulators, particularly in connection with robotics.
On work machines the boom structures are typically placed either in front of the cabin, in other words between the cabin and the working area, or laterally to the cabin. However, both solutions limit the visibility of the machine operator working in the cabin over the working area, in many solutions to a significant extent. Consequently, attempts have been made to design the boom structures such that they limit the field of vision as little as possible, and additionally, the cabin may be arranged rotatable or otherwise movable in relation to the boom structure, whereby the visibility would be limited as little as possible. To arrange the boom structure laterally to the cabin also limits the reach of the boom structure, particularly to the opposite side of the cabin, as well as often limits the visibility considerably on the side of the boom structure and impedes the general stability of the work machine, in particular, in working stage, especially as the boom structure is subjected to powerful forces, for instance, in connection with the handling of heavy objects, and also sometimes in movement/transition stage, wherefore it often limits and controls working to be one-sided.
There are also known some solutions, in which the boom structure is placed behind the cabin in such a manner that the vertical pivoted axle of the boom structure is located behind the cabin in relation to the working direction, whereby the boom structure does not disturb the visibility in the working direction. In that case, however, some of the reach in the actual working direction is lost, and typically, in cabin design, particularly in defining the height of the cabin, it is necessary to pay attention to the limitations set by the boom structure stretching over the cabin. Direct rear visibility is naturally limited and forms a wide blind area. In addition, a rear overhang caused by the boom structure becomes large, especially if the boom structure is arranged to rotate on the same carrier structure with the cabin.